The administration of active agents for control of populations, treatment of disease, and immunization to animals in the wild presents several problems. First, the active agent must be "packaged" in such a manner that the animal toward whom the active agent is targeted will accept the bait with the agent. The active agent must be protected from disintegration or release into the environment before it reaches the desired targeted animal. Furthermore, the "packaging" must deliver the active agent to the appropriate site in the targeted animal so that maximum effect from the active agent will result. Of particular concern is the immunization of animals against diseases that can be transmitted to man or domesticated animals.
Rabies in dogs and in wildlife is an example of a problem that has been addressed by use of baits containing active agents, in this case, the vaccine. The disease is a persistent and widespread problem in North America as well as in many lesser developed countries of the world. In the United States 88% of all rabies cases reported in 1988 occurred in wild animals. Specific economic loss estimates are lacking. However, about 25,000 post-exposure human rabies treatments are given annually at a cost of about 12 to 13 million dollars. Additional economic factors are cost of vaccine production, laboratory diagnosis and fees, compensatory insurance claims, vaccination of pets and livestock, livestock losses, wildlife and fur resource losses, salaries and operating costs associated with handling rabies outbreaks, posting of infected areas, and control of wildlife vectors. Historically, the federal Animal Damage Control Program has participated in the local reduction of wildlife vector populations as authorized under the Animal Damage Control Act of 1931 and, more recently, under the 1988 USDA Appropriations Act. Both acts authorize the conduct of research on rabies and other zootic diseases as worthy of the attention of the federal government.
In order to effectively immunize a species of against rabies five primary factors must be available: (1) an effective vaccine, (2) baits readily accepted by target species, (3) baiting methods that reach a high proportion of the susceptible population, (4) methods and materials that can be used safely, and (5) acceptable costs for development and use.
Recent developments in oral rabies vaccine technology and delivery systems research in Europe, Canada, and, most recently, in the United States indicate an increased potential for controlling the disease in wildlife using new vaccines. The vaccination approach has biological advantages over population reduction and is far more acceptable to the public, particularly in urban areas of the United States. In addition to use for dogs, an oral vaccine may be useful in controlling rabies in, for example, arctic foxes of Alaska, mongooses of the Caribbean Islands, skunks of the Midwest and California, red foxes of the Northeast, and raccoons of the Mid-Atlantic and Southeast.
The concept of immunizing wildlife using an oral rabies vaccine delivered by bait was first tested with captive red foxes in the early 1960's. Subsequent laboratory studies in Europe and the United States showed further potential for orally immunizing the species. An outbreak of rabies in red foxes in norther Europe that spread through various countries during the 1950-1970's stimulated parallel vaccination studies in Switzerland and West Germany. Canada, Switzerland, West Germany and, more recently, France undertook field studies to determine the potential for baiting fox populations by distributing baits containing physiological markers that indicated which individual animals took baits. Collection of foxes following baiting established that high percentages of target populations had consumed baits. The oral immunization concept found favor in Europe because previously used conventional population reduction techniques such as den destruction and hunting did not appear efficacious for stopping fox rabies. European field studies using baits with markers were followed by widespread application of baits containing rabies vaccine. These efforts have reportedly eliminated fox rabies in most of Switzerland and parts of West Germany. France and Belgium have also initiated field evaluations.
Previous baits used have been described in the patent literature. U.S. Pat. No. 4,014,991 assigned to the U.S. Government describes a plastic elongated polyethylene tube holding attenuated vaccine. The vaccine containing bait of that invention is an ampule surrounded by a meat bait. When the bait is bitten, the vaccine is transferred to the buccal mucosa.
U.S. Pat. No. 4,650,673 of Johnston discloses a sponge that is saturated with liquid vaccine so that significant volumes of the vaccine are expelled upon bite penetration. The sponge vector is coated with a wax containing an attractant such as beef fat. The sponge is filled with vaccine by injection into the sponge. The sponge does not surround the vaccine, but is impregnated with it. The covering is a water-proof wax with attractant. The preferred shape of the baits is cubical.
U.S. Pat. No. 4,752,474 describes and claims an oral vaccine. The primary emphasis of the disclosure is on the vaccine itself. It is simply stated that the vaccine was administered in baits. The particular baits used are not described.
U.S. Pat. No. 4,861,586 describes a prefabricated animal bait wherein the active agent is enveloped by a carrier comprising a fat material and at least one additive to stabilize the shape retention of the bait wherein the lure (attractant), fat, and additive are made into a thick paste. No teaching regarding use of an ampule is disclosed.